(a) Field of the Invention
The present invention relates to a liquid crystal display (LCD) and a driving method thereof. More specifically, the present invention relates to an LCD with an adaptive luminance intensifying function for modifying the luminance of a back light according to images provided on the LCD, and a driving method thereof.
(b) Description of the Related Art
In general, as to features of a cold cathode fluorescent lamp (CCFL) used for a light source in an LCD, its luminance is inversely proportional to its lifetime. That is, if the CCFL is driven with a high current to increase the luminance, its lifespan is reduced, and if the CCFL is driven at a low current to increase its lifetime, it is difficult to obtain high luminance. However, actual commercial products generally require high luminance and a long lifetime concurrently.
To satisfy these dual requirements, an LCD panel generally is driven at a predetermined level of luminance, and in the case of driving a screen that requires a specific high luminance, a high current is temporarily provided to a backlighting lamp so as to increase active regions of the luminance of a display element.
Also, the current used by the display elements is varied according to images displayed on the LCD screen. For example, in the case of a normally white mode wherein liquid crystal molecules are rearranged in the electric field direction when the voltage is provided and incident rays are isolated, when the number of bright pixels on the screen is increased, the power consumed by the panel is reduced, and when the number of dark pixels on the screen is increased, the power consumed by the panel is increased. A method for controlling the current of the lamp according to the power consumed by the panel mainly uses this feature.
The above-noted technique, requires an additional circuit for detecting the current consumed by the panel and modifying the current to fit a variation range of a luminance control signal of a back light driving inverter.
Also, since the luminance of all the screen is controlled, much power is used compared to only controlling the luminance of a needed screen portion.